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Exercise intensity affects many potential postprandial responses, but there is limited information on the influence of exercise modality. Therefore, the aim of this study was to investigate if the nature of exercise at two different intensities would affect gastric emptying rate (GER), appetite and metabolic responses following ingestion of a semi-solid meal. Twelve healthy men completed, in a random order, four 60-min cycles at 60% VO2peak (MOD), 40% VO2peak (LOW) and in a continuous (CON) or intermittent (INT) manner. INT consisted of 20 &times, 1-min exercise bouts with 2-min rest breaks. INT and CON were matched for total work output at each intensity. GER of the post-exercise meal was measured for 2 h using the 13C-breath method. Blood glucose, substrate utilisation and appetite ratings were measured at regular intervals throughout all trials and 24-h energy intake (EI) post-trials was assessed. GER-Delta over Baseline (DOB) was lower (p &lt, 0.05) on MOD-INT vs. MOD-CON from 30&ndash, 120 min post-meal. Blood glucose was higher mid-exercise (p &lt, 0.05) on MOD-INT vs. MOD-CON. Although post-exercise LOW-CON was significantly higher than LOW-INT (p &lt, 0.05), blood glucose was also higher 30-min post-meal ingestion on both CON trials compared to INT (p &lt, 0.001). No interaction effect was observed for perceived appetite responses 2 h after meal ingestion (all p &gt, 0.05). 24-h post-trial EI was similar between LOW-CON vs. LOW-INT (p &gt, 0.05), although MOD-INT vs. MOD-CON 3500 &plusmn, 1419 vs. 2556 &plusmn, 989 kCal: p &lt, 0.001 was elevated. In summary, MOD-INT exercise delays GER without stimulating perceived appetite in the 2 h period after meal ingestion, although EI was greater in the 24-h post-trial.

Health effects of orally ingested bioactive compounds can only occur if bioactive molecules are absorbed and transported to target tissues. Paradoxically, many foods are rich in micronutrients but intestinal absorption is often limited. Immediately after absorption, lipid soluble nutrients are packaged into chylomicrons (CM), therefore quantification of the micronutrient content in CM has been used as tool to evaluate bioavailability(1). For bioavailability studies the isolated CM fraction must not contain liver derived lipoproteins (VLDL, LDL) since only intestine derived CM carry recently absorbed lipids and lipophilic micronutrients. As isolated CM can be contaminated with liver derived lipoproteins, this study evaluated the purity of collected CM and VLDL fractions. Each CM contains one apolipoprotein B-48 (apoB-48) and each VLDL contains one apolipoprotein B-100 (apoB-100) on its surface(2) therefore purity of CM and VLDL fractions was evaluated via the presence/absence of apoB-100 and apoB-48.CM and VLDL fractions were isolated as previously described(1,3)from whole plasma collected at 0, 2, 4 or 6 h after participants consumed a lipid (15.4g) and carotenoid (36mg) rich smoothie (480mL). Plasma density was adjusted to 1.1g/mL with KBr (0.14g/mL), placed in ultracentrifugation tubes (38 mL, thickwall) and overlaid with 3 solutions containing NaCl, KBr and Na-EDTA with densities of 1.020, 1.065 and 1.006g/mL.CM fraction was collected after ultracentrifugation at 25,000 rpm for 34 min in a Beckman Coulter Optima XE-90 with SW32Ti swinging bucket rotor. VLDL fraction was collected after additional 102 min at 25,000 rpm.ELISA analysis revealed that apoB-48 and apoB-100 were present in both CM and VLDL fractions. Less than 0.1% of plasma apoB-48 (< 98pmol/L) was present in CM or VLDL fraction. Less than 0.3% (< 2,425pmol/L) and 4% (< 54,124pmol/L) of plasma apoB-100 was present in CM and VLDL fractions, respectively. Low recoveries of apoB-48 and apoB-100 in CM and VLDL fraction suggests that ultracentrifugation neither concentrated nor isolated CM or VLDL. While ourapoB-48 and apoB-100 results agree with previously reported values in plasma, CM and VLDL(3,4), no previous study evaluated apoB-48 and apoB-100 recovery from plasma.

The purpose of this study was to examine the efficacy of water and a 50 mmol/L NaCl solution on postexercise rehydration when a standard meal was consumed during rehydration. Eight healthy participants took part in two experimental trials during which they lost 1.5 ± 0.4% of initial body mass via intermittent exercise in the heat. Participants then rehydrated over a 60-min period with water or a 50 mmol/L NaCl solution in a volume equivalent to 150% of their body mass loss during exercise. In addition, a standard meal was ingested during this time which was equivalent to 30% of participants predicted daily energy expenditure. Urine samples were collected before and after exercise and for 3 hr after rehydration. Cumulative urine volume (981 ± 458 ml and 577 ± 345 mL; p = .035) was greater, while percentage fluid retained (50 ± 20% and 70 ± 21%; p = .017) was lower during the water compared with the NaCl trial respectively. A high degree of variability in results was observed with one participant producing 28% more urine and others ranging from 18–83% reduction in urine output during the NaCl trial. The results of this study suggest that after exercise induced dehydration, the ingestion of a 50 mmol/L NaCl solution leads to greater fluid retention compared with water, even when a meal is consumed postexercise. Furthermore, ingestion of plain water may be effective for maintenance of fluid balance when food is consumed in the rehydration period.

Growing evidence suggests circadian rhythms, nutrition and metabolism are intimately linked. Intermittentfasting (IMF) has become an increasingly popular intervention for metabolic health and combining IMF withexercise may lead to benefits for weight management. However, little is known about the diurnal variation offasted exercise. This study aimed to investigate the diurnal influences on gastric emptying rate (GER), metabolicresponses, and appetite to fasted and non-fasted exercise. Twelve healthy males completed four 45 min walks ina randomised order. Walks were completed in the morning (AM) and evening (PM) and either fasted (FASTED)or after consumption of a standardised meal (FED). GER of a semi-solid lunch was subsequently measured for 2 husing the13C breath test. Blood glucose concentration, substrate utilisation, and ratings of appetite were mea-sured throughout. Energy intake was also assessed for the following 24 h. GER Tlagwas slower in PM-FASTEDcompared to AM-FASTED, AM-FED, and PM-FED (75 ± 18 min vs. 63 ± 14 min,P= 0.001, vs. 65 ± 10 min,P= 0.028 and vs. 67 ± 16 min,P= 0.007). Blood glucose concentration was greater in the FED trials incomparison to the FASTED trials pre-lunch (P< 0.05). Fat oxidation was greater throughout exercise in bothFASTED trials compared to FED, and remained higher in FASTED trials than fed trials post-exercise until 30 minpost-lunch ingestion (allP< 0.05). No differences were found for appetite post-lunch (P> 0.05) or 24 h post-energy intake (P= 0.476). Thesefindings suggest that evening fasted exercise results in delayed GER, withoutchanges in appetite. No compensatory effects were observed for appetite, and 24 h post-energy intake for bothfasted exercise trials, therefore, increased fat oxidation holds positive implications for weight management.

Whey protein is a commonly ingested nutritional supplement amongst athletes and regular exercisers, however, its role in post-exercise rehydration remains unclear. Eight healthy male and female participants completed two experimental trials involving the ingestion of 35 g of whey protein (WP) or maltodextrin (MD) at the onset of a rehydration period, followed by ingestion of water to a volume equivalent to 150% of the amount of body mass lost during exercise in the heat. The gastric emptying rates of the solutions were measured using 13C breath tests. Recovery was monitored for a further 3 h by the collection of blood and urine samples. The time taken to empty half of the initial solution (T1/2) was different between the trials (WP = 65.5 &plusmn, 11.4 min, MD = 56.7 &plusmn, 6.3 min, p = 0.05), however, there was no difference in cumulative urine volume throughout the recovery period (WP = 1306 &plusmn, 306 mL, MD = 1428 &plusmn, 443 mL, p = 0.314). Participants returned to net negative fluid balance 2 h after the recovery period with MD and 3 h with WP. The results of this study suggest that whey protein empties from the stomach at a slower rate than MD, however, this does not seem to exert any positive or negative effects on the maintenance of fluid balance in the post-exercise period.

Little data exists on drinking behavior, sweat loss, and exercise intensity across a competitive handball tournament in elite female athletes. Heart rate (HR), fluid balance and sweat electrolyte content were assessed on 17 international players across a 6-day tournament involving 5 games and 2 training sessions played indoors (23 ± 2 °C, 30 ± 2% relative humidity). Active play (effective) mean HR was 155 ± 14 bpm (80 ± 7.5% HRmax) with the majority of time (64%) spent exercising at intensities >80% HRmax. Mean (SD) sweat rates during games were 1.02 ± 0.07 L · h-1 and on 56% of occasions fluid intake matched or exceeded sweat loss. A significant relationship was observed between estimated sweat loss and fluid intake during exercise (r2 = .121, p = .001). Mean sweat sodium concentration was 38 ± 10 mmol · L-1, with significant associations observed between player sweat rates and time spent exercising at intensities >90% HRmax (r2 = .181, p = .001). Fluid and electrolyte loss appear to be work rate dependent in elite female handball players, whom appear well capable of replacing fluids lost within a tournament environment. Due to large between-athlete variations, a targeted approach may be warranted for certain players only.

Angiotensin converting enzyme (ACE) and bradykinin receptor B2 (B2R) genetic variation may affect thirst because of effects on angiotensin II production and bradykinin activity, respectively. To examine this, 45 healthy Caucasian men completed 60 min of cycle exercise at 62% ± 5% peak oxygen uptake in a room heated to 30.5 ± 0.3 °C with ad libitum fluid intake. Blood samples were collected pre-, mid-, and immediately post-cycle. Fluid intake, body mass loss (BML), sweat loss (determined via changes in body mass and fluid intake), and thirst sensation were recorded. All participants were genotyped for the ACE insert fragment (I) and the B2R insert sequence (P). Participants were homozygous for the wild-type allele (WW or MM), heterozygous (WI or MP) or homozygous for the insert (II or PP). No differences between genotype groups were found in mean (±SD) voluntary fluid intake (WW: 613 ± 388, WI: 753 ± 385, II: 862 ± 421 mL, p = 0.31; MM: 599 ± 322, MP: 745 ± 374, PP: 870 ± 459 mL, p = 0.20), percentage BML or any other fluid balance variables for both the ACE and B2R genes, respectively. Mean thirst perception in the B2R PP group, however, was higher (p < 0.05) than both MM and MP at 30, 45, and 60 min. In conclusion, the results of this study suggest that voluntary fluid intake and fluid balance in healthy men performing 60 min of moderate-intensity exercise in the heat are not predominantly influenced by ACE or B2R genetic variation.

The rate-limiting step to the oxidation of ingested carbohydrate is the rate at which it is absorbed from the intestine. Glucose is absorbed via SGLT-1 transporters with the rate of absorption determined by the number of transporters present. Animal studies have indicated that the number of transporters can be increased when dietary carbohydrate intake is increased and when the intestine is exposed to artificial sweeteners. Human studies have not observed any effect of this strategy on carbohydrate oxidation during relatively low intensity exercise. In this study, 10 healthy male and female participants (22±1 y; 69±12 kg; 176±10 cm) undertook two experimental trials involving 90 min of cycle exercise at an intensity of 70% heart rate reserve. In the two hours prior to exercise, participants ingested 400 mL of water (W) or 400 mL of water containing 159 mg of sucralose (S) in equal aliquots every 15 min. 500 mL of a commercially available sports drink, containing 75 mg of 13C glucose, was ingested before the start of exercise. Breath samples were collected at the start of each trial, before sports drink ingestion and at 15 min intervals throughout exercise and analysed for 13C:12C ratio. Average power output (W=148±26; S=140±36 watts) and heart rate (W=157±4; S=155±6 bpm) during exercise were similar (p>0.05) between trials. Delta Over Baseline (DOB) 13C:12C values showed a main effect of trial (p=0.016), time (p

Nutritional supplement use in elite athletes is widespread despite a lack of evidence supporting beneficial effects of many of these substances. Little is known, however, about the use of nutritional supplements or performance enhancing drugs (PEDs) in non-elite recreational exercisers. In this study, 114 regular exercisers voluntarily and anonymously completed a basic questionnaire outlining their use, type, reasons for use as well as purchase and information source regarding nutritional supplements. Additionally, participants were asked if they had been offered PED and, if so, what they had been offered. In total, 72% of participants indicated that they regularly used nutritional supplements. Of these, 12% reported taking only one supplement with 76% reporting taking 2–4 supplements and 12% reporting taking five or more supplements. Protein or amino acid powder (74%), sports drinks (69%), creatine (46%) and multivitamins (46%) were the most commonly reported supplements. 90% of supplement users reported multiple reasons for use with providing energy (67%), improving performance (62%) and increasing strength (57%) the main reasons given. The internet (65%) was the most common place supplements were purchased from followed by a nutrition shop in person (55%). The internet was the most common place (76%) that information regarding supplements was obtained followed by friends or family (36%) and the product label (30%). Of the 114 respondents, 28% reported having been offered PEDs with 91% of these being offered anabolic steroids. In total, only 7 respondents (6%) reported having taken PEDs. The results of this study suggest that the use of nutritional supplements is very common amongst non-elite recreational exercisers. Many people obtain both information and products from the internet which increases the risk of inaccurate information and the chances of contaminated supplements being purchased.

The purpose of this study was to examine the gastric emptying and rehydration effects of hypotonic and hypertonic glucose-electrolyte drinks after exercise-induced dehydration. Eight healthy males lost ~1.8% body mass by intermittent cycling and rehydrated (150% of body mass loss) with a hypotonic 2% (2% trial) or a hypertonic 10% (10% trial) glucose-electrolyte drink over 60 min. Blood and urine samples were taken at preexercise, postexercise, and 60, 120, 180, and 240 min postexercise. Gastric and test drink volume were determined 15, 30, 45, 60, 90, and 120 min postexercise. At the end of the gastric sampling period 0.3% (2% trial) and 42.1% (10% trial; p < .001) of the drinks remained in the stomach. Plasma volume was lower (p < .01) and serum osmolality was greater (p < .001) at 60 and 120 min during the 10% trial. At 240 min, 52% (2% trial) and 64% (10% trial; p < .001) of the drinks were retained. Net fluid balance was greater from 120 min during the 10% trial (p < .001). When net fluid balance was corrected for the volume of fluid in the stomach, it was greater at 60 and 120 min during the 2% trial (p < .001). These results suggest that the reduced urine output following ingestion of a hypertonic rehydration drink might be mediated by a slower rate of gastric emptying, but the slow gastric emptying of such solutions makes rehydration efficiency difficult to determine in the hours immediately after drinking, compromising the calculation of net fluid balance.

Water is the most abundant chemical constituent of the human body, typically making up approximately two thirds of body mass, but body water content is maintained within relatively narrow limits by a number of regulatory mechanisms. Both a reduction (hypohydration) and increase (hyperhydration) in body water may, if sufficiently severe, lead to adverse health and performance consequences. Active lifestyles, warm climates, and high altitude, as well as some infectious illnesses, increase the likelihood of becoming hypohydrated due to an increase in water loss. Moderate reductions in body water result in changes in cardiovascular system function as well as altering cognitive function and mood. A significant number of elite athletes, recreational exercisers and those with active occupations begin their daily activities in a hypohydrated state and incur large sweat losses during periods of activity, and thus risk negative effects on physiological function. Sweat rate and fluid intake during physical exertion are highly variable between individuals, suggesting that an individual hydration strategy may be necessary to avoid significant levels of hypohydration. Rehydration after the completion of physical activity may also be necessary to avoid starting further bouts of activity in a hypohydrated state. Undertaking physical activity in a hypohydrated state appears to increase an individual’s perceived exertion which may negatively influence exercise performance and self-selected exercise intensity, and may decrease the likelihood of further participation in physical activity. This is, therefore, an important consideration for public health as well as competitive sportspeople, be they elite or otherwise. Certain populations, such as the elderly, are more likely to become hypohydrated, which may lead to other illnesses and contribute to morbidity and mortality.

Hypohydration, or a body water deficit, is a common occurrence in athletes and recreational exercisers following the completion of an exercise session. For those who will undertake a further exercise session that day, it is important to replace water losses to avoid beginning the next exercise session hypohydrated and the potential detrimental effects on performance that this may lead to. The aim of this review is to provide an overview of the research related to factors that may affect postexercise rehydration. Research in this area has focused on the volume of fluid to be ingested, the rate of fluid ingestion, and fluid composition. Volume replacement during recovery should exceed that lost during exercise to allow for ongoing water loss; however, ingestion of large volumes of plain water results in a prompt diuresis, effectively preventing longer-term maintenance of water balance. Addition of sodium to a rehydration solution is beneficial for maintenance of fluid balance due to its effect on extracellular fluid osmolality and volume. The addition of macronutrients such as carbohydrate and protein can promote maintenance of hydration by influencing absorption and distribution of ingested water, which in turn effects extracellular fluid osmolality and volume. Alcohol is commonly consumed in the postexercise period and may influence postexercise rehydration, as will the coingestion of food. Future research in this area should focus on providing information related to optimal rates of fluid ingestion, advisable solutions to ingest during different duration recovery periods, and confirmation of mechanistic explanations for the observations outlined.

Context: Many active people finish exercise hypohydrated, so effective rehydration after exercise is an important consideration. Objective: To determine the effects of a rehydration solution containing whey protein isolate on fluid balance after exercise-induced dehydration. Design: Randomized controlled clinical trial. Setting: University research laboratory. Patients or Other Participants: Twelve healthy men (age = 21 ± 1 years, height = 1.82 ± 0.08m, mass = 82.71 ± 10.31 kg) participated. Intervention(s): Participants reduced body mass by 1.86% ± 0.07% after intermittent exercise in the heat and re-hydrated with a volume of drink in liters equivalent to 1.5 times their body mass loss in kilograms of a solution of either 65 g/L carbohydrate (trial C) or 50 g/L carbohydrate and 15 g/L whey protein isolate (trial CP). Solutions were matched for energy density and electrolyte content. Urine samples were collected before and after exercise and for 4 hours after rehydration. Main Outcome Measure(s): We measured urine volume, drink retention, net fluid balance, urine osmolality, and subjective responses. Drink retention was calculated as the difference between the volume of drink ingested and urine produced. Net fluid balance was calculated from fluid gained through drink ingestion and fluid lost through sweat and urine production. Results: Total cumulative urine output after rehydration was not different between trial C (1173 ± 481 mL) and trial CP (1180 ± 330 mL) (F1 = 0.002, P = .96), and drink retention during the study also was not different between trial C (50% ± 18%) and trial CP (49% ± 13%) (t11 = −0.159, P = .88). At the end of the study, net fluid balance was negative compared with base-line for trial C (−432 ± 436 mL) (t11 = 3.433, P = .03) and trial CP (−432 ± 302 mL) (t11 = 4.958, P = .003). Conclusions: When matched for energy density and electrolyte content, a solution of carbohydrate and whey protein isolate neither increased nor decreased rehydration compared with a solution of carbohydrate.

This study investigated the acute circulating gut hormone, appetite and gastric emptying rate responses to a semi-solid meal following exercise at different intensities. Twelve men completed three trials in a randomised-crossover design, consisting of continuous cycling at 70% V˙O2Peak (HIGH), 40% V˙O2Peak (LOW) or rest (CONTROL). Baseline samples were collected after an overnight fast before undertaking the 60 min exercise or rest period, followed by 30 min rest before consumption of a standardised semi-solid meal (~242 kcal). During the 2 h postprandial period, gastric emptying rate of the meal was examined using the 13C-breath test method, appetite was measured using visual analogue scales, and serum concentrations of acylated ghrelin, pancreatic polypeptide, peptide YY, glucagon-like peptide-1, insulin, glucose, triglycerides, total cholesterol and non-esterified fatty acids were assessed. Subjective appetite response was not different between trials (p &gt, 0.05). Half emptying time of the meal was 89 &plusmn, 13, 82 &plusmn, 8 and 94 &plusmn, 31 min on CONTROL, LOW and HIGH, respectively (p = 0.247). In healthy un-trained adult males, responses to exercise at intensities of 70% and 40% V˙O2Peak did not differ to a non-exercise control for measurements of subsequent gastric emptying, circulating gut hormone response or appetite. These results suggest that exercise intensity has little effect on post-exercise appetite response to a semi-solid meal.

The effectiveness of different carbohydrate solutions in restoring fluid balance in situations of voluntary fluid intake has not been examined previously. The effect of the carbohydrate content of drinks ingested after exercise was examined in 6 males and 3 females previously dehydrated by 1.99 ± 0.07% of body mass via intermittent exercise in the heat. Beginning 30 min after the cessation of exercise, subjects drank ad libitum for a period of 120 min. Drinks contained 31 mmol·L–1 Na+ as NaCl and either 0%, 2%, or 10% glucose with mean ± SD osmolalities of 74 ± 1, 188 ± 3, and 654 ± 4 mosm·kg–1, respectively. Blood and urine samples were collected before and after exercise, midway through rehydration, and throughout a 5 h recovery period. Total fluid intake was not different among trials (0%: 2258 ± 519 mL; 2%: 2539 ± 436 mL; 10%: 2173 ± 252 mL; p = 0.173). Urine output was also not different among trials (p = 0.160). No differences among trials were observed in net fluid balance or in the fraction of the ingested drink retained. In conclusion, in situations of voluntary fluid intake, hypertonic carbohydrate-electrolyte solutions are as effective as hypotonic carbohydrate-electrolyte solutions at restoring whole-body fluid balance.

Previous investigations have suggested that exercise at intensities greater than 70% maximal oxygen uptake (VO2max) reduces gastric emptying rate during exercise, but little is known about the effect of exercise intensity on gastric emptying in the postexercise period. To examine this, 8 healthy participants completed 3 experimental trials that included 30 min of rest (R), low-intensity (L; 33% of peak power output) exercise, or high-intensity (H; 10 × 1 min at peak power output followed by 2 min rest) exercise. Thirty minutes after completion of exercise, participants ingested 595 ml of a 5% glucose solution, and gastric emptying rate was assessed via the double-sampling gastric aspiration method for 60 min. No differences (p > .05) were observed in emptying characteristics for total stomach volume or test meal volume between the trials, and the quantity of glucose delivered to the intestine did not differ between trials (p > .05). Half-emptying times did not differ (p = .902) between trials and amounted to 22 ± 9, 22 ± 9, and 22 ± 7 min (M ± SD) during the R, L, and H trials, respectively. These results suggest that exercise has little effect on postexercise gastric emptying rate of a glucose solution.

Objective Short-term dietary glucose supplementation has been shown to accelerate the gastric emptying rate of both glucose and fructose solutions. The aim of this study was to examine gastric emptying rate responses to monosaccharide ingestion following short-term dietary fructose supplementation. Methods The gastric emptying rate of a fructose solution containing 36 g of fructose and an equicaloric glucose solution containing 39.6 g glucose monohydrate were measured in 10 healthy non-smoking men with and without prior fructose supplementation (water control) using a randomized crossover design. Gastric emptying rate was assessed for a period of 1 h using the [13C]breath test with sample collections at baseline and 10-min intervals following drink ingestion. Additionally, appetite ratings of hunger, fullness, and prospective food consumption were recorded at baseline and every 10 min using visual analog scales. Results Increased dietary fructose ingestion resulted in significantly accelerated half-emptying time of a fructose solution (mean = 48, SD = 6 versus 58, SD = 14 min control; P = 0.037), whereas the emptying of a glucose solution remained unchanged (mean = 85, SD = 31 versus 78, SD = 27 min control; P = 0.273). Time of maximal emptying rate of fructose was also significantly accelerated following increased dietary fructose intake (mean = 33, SD = 6 versus 38, SD = 9 min control; P = 0.042), while it remained unchanged for glucose (mean = 45, SD = 14 versus 44, SD = 14 min control; P = 0.757). No effects of supplementation were observed for appetite measures. Conclusion Three d of supplementation with 120 g/d of fructose resulted in an acceleration of gastric emptying rate of a fructose solution but not a glucose solution.

The present study investigated the relationship between the milk protein content of a rehydration solution and fluid balance after exercise-induced dehydration. On three occasions, eight healthy males were dehydrated to an identical degree of body mass loss (BML, approximately 1·8 %) by intermittent cycling in the heat, rehydrating with 150 % of their BML over 1 h with either a 60 g/l carbohydrate solution (C), a 40 g/l carbohydrate, 20 g/l milk protein solution (CP20) or a 20 g/l carbohydrate, 40 g/l milk protein solution (CP40). Urine samples were collected pre-exercise, post-exercise, post-rehydration and for a further 4 h. Subjects produced less urine after ingesting the CP20 or CP40 drink compared with the C drink (Psd 12) %) and CP40 (64 (sd 6) %) drinks had been retained compared with the C drink (46 (sd 9) %) (Psd 154) ml) compared with both trials CP20 ( − 181 (sd 280) ml) and CP40 ( − 107 (sd 126) ml) (PP

Ingestion of carbohydrate during exercise is common in order to provide an exogenous substrate for oxidation and to improve performance. The rate at which a solution is emptied from the stomach is an important step in this process. Acute changes in blood glucose concentration significantly influence gastric emptying rate (GER). Animal studies have suggested that exposing the intestine to glucose and artificial sweeteners leads to an increase in mRNA transcription and the number of SGLT-1 transporters within the intestine. This may influence the rate of glucose absorption and GER. The aim of this study was to investigate the effects of pre-exercise sucralose ingestion on GER during exercise. Nine healthy males volunteered to participate in this study, which involved completion of two experimental trials undertaken in a fasted state. Over a two hour period, participants ingested 400 mL of water (C) or 400 mL of water containing 159 mg sucralose (S) in equal aliquots every 15 minutes. Following this, 600 mL of a commercially available carbohydrate-electrolyte solution containing 100 mg 13C sodium acetate was ingested prior to undertaking 90 minutes of cycle exercise at 70% of heart rate reserve. Breath samples were collected pre- ingestion and at 15 minute intervals throughout exercise for measurement of GER. No differences (P>0.05) were observed between trials in heart rate or rating of perceived exertion during exercise. Half emptying time of the solution was 47±16 (C) and 44±15 (S) minutes (P=0.555) while time of maximum rate of gastric emptying was 39±10 (C) and 34±10 (S) minutes (P=0.160). No difference (P>0.05) between the trials was observed in delta over baseline breath values. The results of this study indicate that pre-exercise sucralose ingestion does not influence GER during exercise. This may be due to the time period of sucralose ingestion not being sufficient for adaptation to occur.

The addition of carbohydrate to drinks designed to have a role in rehydrating the body is commonplace. The gastric emptying and fluid uptake characteristics following repeated ingestion of drinks with high and low glucose concentrations were examined in eight subjects (three male and five female). Following a 13 h fluid restriction period, the subjects ingested a volume of test solution amounting to 3 % of the initial body mass over a period of 60 min. Test drinks were 2 and 10 % glucose–electrolyte solutions with osmolalities of 189 (sd 3) and 654 (sd 3) mOsm/kg, respectively. The initial bolus of each test solution contained 10 g of 2H2O. Blood samples were collected throughout drinking and for 60 min afterwards. Gastric volumes were determined via gastric aspiration at 15 min intervals for 120 min. No difference between trials in total stomach volume was observed until 30 min after the ingestion of the first bolus of test drink, but blood 2H concentration was increased during both trials 10 min after ingestion of the first bolus. Blood 2H concentration was greater at this time point during the 2 % glucose trial than during the 10 % glucose trial and remained higher for the duration of the trial with the exception of one time point. Urine volume at the end of the trial was greater in the 2 % glucose trial than in the 10 % glucose trial. It is concluded that the reduced overall rate of fluid uptake following ingestion of the 10 % glucose solution was due largely to a relatively slow rate of gastric emptying.

The present study examined the effects of milk protein on rehydration after exercise in the heat, via the comparison of energy- and electrolyte content-matched carbohydrate and carbohydrate–milk protein solutions. Eight male subjects lost 1·9 (sd 0·2) % of their body mass by intermittent exercise in the heat and rehydrated with 150 % of their body mass loss with either a 65 g/l carbohydrate solution (trial C) or a 40 g/l carbohydrate, 25 g/l milk protein solution (trial CP). Urine samples were collected before and after exercise and for 4 h after rehydration. Total cumulative urine output after rehydration was greater for trial C (1212 (sd 310) ml) than for trial CP (931 (sd 254) ml) (P sd 12) %) than that after ingestion of drink C (43 (sd 15) %) (P P sd 0·27) litres) than for trial C ( − 0·52 (sd 0·30) litres), and although net negative for both the trials, it was only significantly negative after ingestion of drink C (P

Heart rate was measured in 79 young male soccer players during training in the third week of Ramadan. Forty-eight players were practising Ramadan fasting, while the other 31 players were eating normally. All participants trained for 60-80 min at an ambient temperature of 25-28 degrees C and relative humidity of 50-53%. Heart rate, which was measured throughout the training session, was marginally higher in the fasting (mean 144 beats . min(-1), s = 25) than in the non-fasting (139 beats . min(-1), s = 23) group (P0.001). When assessed as the percentage of heart rate reserve utilized, however, the training load was similar for both groups (62%, s = 8). No difference was detected in training intensity for the fasting and non-fasting groups when quantified by either training impulse (253, s = 139 and 253, s = 108, respectively) or training load indicator (222, s = 123 and 179, s = 49, respectively). The overall subjective rating of perceived exertion of the training session reported 20 min after finishing training was similar for the fasting (12, range 6-17) and non-fasting (12, range 7-17) groups, which was comparable (P = 0.16) to the mean value for the entire week (13, range 8-16). A similar finding was observed in the players' subjective appraisal of the difficulty of training of the individual session and for the whole week's training. Overall exercise load measures indicated that there was no biologically significant difference between the fasting and non-fasting groups during training in the third week of Ramadan.

The change in blood and plasma volume following ingestion of glucose solutions of varying concentrations was estimated in twelve healthy male volunteers. Subjects consumed, within a 5 min period, 600 ml of a solution containing 0, 2, 5 or 10 % glucose with osmolalities of 0 (sd 0), 111 (sd 1), 266 (sd 7) and 565 (sd 5) mOsm/kg, respectively. Blood samples were collected over the course of 1 h after ingestion at intervals of 10 min. After ingestion of the 2 % glucose solution, plasma volume increased from baseline levels at 20 min. Plasma volume decreased from baseline levels at 10 and 60 min after ingestion of the 10 % glucose solution. Heart rate was elevated at 10 and 60 min after ingestion of the 10 % glucose solution and decreased at 30 and 40 min after ingestion of the 2 % glucose solution relative to the average heart rate recorded before drinking. It is concluded that ingestion of hypertonic, energy-dense glucose solutions results in a decrease in plasma and extracellular fluid volume, most likely due to the net secretion of water into the intestinal lumen.

Objective This study investigated the effect of the osmolality and carbohydrate content of drinks on their rehydration effectiveness after exercise-induced dehydration. Methods Six healthy male volunteers were dehydrated by 1.9 ± 0.1% of body mass by intermittent cycle ergometer exercise in the heat before ingesting one of three solutions with different carbohydrate contents and osmolalities over a period of 1 h. Thirty minutes after the cessation of exercise, subjects drank a volume that amounted to 150% (130–150, median [range]) of their body mass loss. Drinks contained 25 mmol/L Na + and 0%, 2%, or 10% glucose with osmolalities of (mean ± SD) 79 ± 4, 193 ± 5, and 667 ± 12 mosm/kg, respectively. Blood and urine samples were collected before exercise, after exercise, and 0, 1, 2, 3, 4, and 6 h after the end of the rehydration period. Results Significantly more of the ingested fluid was retained in the 10% trial (46 ± 9%) than in the 0% trial (27 ± 13%), with 40 ± 14% retained in the 2% trial. Subjects remained euhydrated for 1 h longer in the 10% glucose trial than in the 2% glucose trial. In the 2% glucose trial, plasma volume was elevated immediately after and 1 h after rehydration. Conclusion This study suggests that, following the rehydration protocol used, hypertonic glucose-sodium drinks may be more effective at restoring and maintaining hydration status after sweat loss than more dilute solutions when the sodium concentration is comparable.

Fluid balance and sweat electrolyte losses were measured in the players and substitutes engaged in an English Premier League Reserve competitive football match played at an ambient temperature of 6–8 °C (relative humidity 50–60%). Intake of water and/or sports drink and urine output were recorded, and sweat composition was estimated from absorbent swabs applied to 4 skin sites for the duration of the game. Body mass was recorded before and after the game. Data were obtained for 22 players (age 21 y, height 180 cm, mass 78 kg) and 9 substitutes (17 y, 181 cm, 72 kg). All were male. Two of the players were dismissed during the game, and none of the substitutes played any part in the game. Mean ± SD sweat loss of players amounted to 1.68 ± 0.40 L, and mean fluid intake was 0.84 ± 0.47 L (n = 20), with no difference between teams. Corresponding values for substitutes, none of whom played in the match, were 0.40 ± 0.24 L and 0.78 ± 0.46 L (n = 9). Prematch urine osmolality was 678 ± 344 mOsm/kg: 11 of the 31 players provided samples with an osmolality of more than 900 mOsm/kg. Sweat sodium concentration was 62 ± 13 mmol/L, and total sweat sodium loss during the game was 2.4 ± 0.8 g. These descriptive data show a large individual variability in hydration status, sweat losses, and drinking behaviors in a competitive football match played in a cool environment, highlighting the need for individualized assessment of hydration status to optimize fluid-replacement strategies.

Exercise performance may be impaired following reductions in body water amounting to approximately 2% body mass. Post-exercise rehydration is an important factor to consider when a subsequent bout of exercise is to be undertaken. Drink volume and composition are important considerations with regards to fluid retention after exercise. The aim of this study was to examine retention of a sports drink and water when consumed with food in the post-exercise period. Seven healthy participants (3 male, 4 female) aged 21–41 y were dehydrated by (mean ± SD) 1.6 ± 0.3% body mass by intermittent cycling in the heat (35.0 ± 0.9°C, 51 ± 7% relative humidity). Participants then consumed a volume equal to 150% body mass loss of a commercially available sports drink or water with a standard meal designed to provide 30% of estimated daily energy expenditure. The drink was consumed in four equal boluses over a period of one hour with the meal consumed with the final three boluses. Urine volume and osmolality were measured before and after exercise and at hourly intervals for three hours after completion of the rehydration period. No significant differences between trials were observed for percentage body mass loss (p = 0.405), sweat loss (p = 0.376) or drink volume (p = 0.371). Cumulative urine volume following rehydration amounted to 765 ± 223 ml and 630 ± 231 ml (p = 0.244) and percentage of drink volume retained amounted to 53 ± 13% and 59 ± 15% (p = 0.336) during the water and sports drink trials, respectively. No difference (p > 0.05) in net fluid balance was observed between trials. The results of this study indicate that there is no difference in post-exercise fluid retention between water and a sports drink when consumed with a meal. The addition of a meal during the post-exercise period is likely to reduce the rate of fluid absorption, resulting in reduced urine production. This may explain the lack of a significant difference between trials.

The rate at which ingested fluid is emptied from the stomach is influenced by a number of factors. Exercise at intensities greater than 70% VO 2max has been shown to reduce gastric emptying rates in healthy individuals,1 but to date, no studies have reported the effects of differing exercise intensities on gastric emptying characteristics after the cessation of exercise. Five males and three females participated in this investigation following prior ethical approval. Each subject undertook a measurement of VO 2max and a familiarisation trial before participating in three randomly assigned experimental trials. These included 30 min of rest, continuous cycling at 33% of peak power obtained during the VO 2max test (LI) and ten 1-min sprints at peak power separated by rest periods of 2 min (HI). 30 min after completion of rest or exercise, a gastric tube was inserted and the stomach emptied before ingestion of 595 ml of a 5% glucose solution. Stomach volumes were determined at 10-min intervals for 1 h using the double sampling technique.23 Subjective feelings of hunger were determined before and after rest or exercise, before drinking and at 10-min intervals after drink ingestion. No differences (p>0.05) in subjective feelings of hunger were observed from pre-exercise or pre-ingestion values at any time during the rest or LI trial. Subjective feelings of hunger were significantly reduced (p=0.005) from pre-exercise values during the HI trial but returned to pre-exercise values before fluid ingestion. Mean±SD half emptying times for the test drink were similar (p=0.999) during the three trials: rest 22±10 min; LI 22±8 min HI 22±7 min. Subjective feelings of hunger in the hour after fluid ingestion were negatively correlated with total stomach volume (R 2 (rest) −0.655, p=0.110, LI:−0.897, p=0.006, HI−0.833, p=0.02). Previous investigations have observed that gastrointestinal function appears to be affected during high intensity exercise, but the results of the present study show that gastric emptying was not impaired 30 min after high intensity exercise. Perceived feelings of hunger and gastrointestinal function appear to be closely linked.

Angiotensin I-converting enzyme (ACE) plays a pivotal role in whole body fluid balance and the degradation of bradykinin. A common allelic variant with a 287 base pair insert has been identified on the ACE gene. The homozygous insertion genotype ( II ) corresponds with lower basal serum ACE concentrations compared to the heterozygous ( WI ) and homozygous wild type genotypes ( WW ). Higher circulating levels of ACE may decrease vasodilation; affecting blood flow and sweat loss during exercise. A genotype-independent rise in ACE activity following 20 min of exercise has been reported, but the response to prolonged exercise is unknown. The aim was to examine the influence of ACE genotype on the serum ACE response to exercise in the heat. Healthy Caucasian males ( n =45, 18–45 y) completed 60 min of cycle exercise at (mean ± SD) 62 ± 5% VO 2max in 30.5 ± 0.3°C, with fluid ad libitum . Fluid intake and sweat loss were recorded. Venous blood samples were drawn pre, mid, and postexercise for the determination of serum ACE concentration and ACE genotype. Basal serum ACE concentrations were dependent on ACE genotype ( WW : 215 ± 57 ng.ml -1 ; WI : 158 ± 28 ng.ml -1 ; II : 106 ± 29 ng.ml -1 , P -1 , 166 ± 29 ng.ml -1 and 115 ± 30 ng.ml -1 for WW , WI and II , respectively ( P ACE genotype ( P = 0.321). No differences were found for mean fluid intake ( WW : 613 ± 388 ml; WI : 753 ± 385 ml; II : 862 ± 421 ml, P = 0.31), or sweat loss ( WW : 1013 ± 257 ml; WI : 1048 ± 254 ml; II : 1257 ± 675 ml, P = 0.28). Serum ACE concentration increased independently of ACE genotype within 30 min exercise at 30.5°C. Coupled with the lack of genotype effect on sweat loss and fluid intake, these results suggest ACE genotype plays little role in fluid balance during exercise.

Milk has been shown to be an effective post-exercise rehydration solution, but the specific effects of milk protein on rehydration after exercise are unknown. This study examined the effects of milk protein on rehydration after exercise in the heat, via the comparison of carbohydrate and carbohydrate-milk protein solutions matched in terms of energy density and electrolyte content. Eight male subjects (mean±SD: age 21±3 years, height 1.78±0.08 m, body mass 75.7±11.6 kg) lost 1.9±0.2% of their initial body mass via intermittent exercise in a warm environment (35±0.1°C, 50.9±2.1% RH). Subjects then rehydrated with 150% of their body mass loss over 1 h, with either a 65 g/l carbohydrate solution (C) or a 40 g/l carbohydrate, 25 g/l milk-protein solution (CP). Urine samples were collected before and after exercise and for 4 h after rehydration. After rehydration, total cumulative urine output was greater for trial C (1212±310 ml) than trial CP (931±254 ml) (p